Tsweyren

Hi, sorry for the noob question, but I quit retail Aion not much into 4.0 and wanted to return now to play it. I'm reading the guides now and trying to learn as much as I can, but as a consequence, I've never done steel wall bastion and I'd have a question regarding it. What exactly does premade stand for? I understand that you assembly the alliance and enter with it fully formed at the 81 garrison, but how does it affect the members distribution, rolling etc once inside the dungeon? Many thanks for a clear explanation :)) (Ps. I know I need some gear before I can do it, I just want to learn what I can about the technicalities)